Bug wars

Bug wars

Warmer climates, northern migration signal robust parasite populations
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May 01, 2007

NATIONAL REPORT — Parasites are on the move. Warmer winters, exploding wildlife populations and reforestation are all fueling the trend.

The reality, according to Michael Dryden, DVM, MS, PhD and flea expert from Kansas State University's College of Veterinary Medicine, is that we will never win the war against bugs, but veterinarians can help pet owners keep them outdoors.

In an interview with DVM Newsmagazine, Dryden, a professor of parasitology and renowned author and lecturer, talked about the ecology and trends in parasitology.

DVM: You have spent your entire career researching these parasites. What aspect do you find most fascinating?

Dryden: The biologic resilience of fleas and ticks is remarkable.


Dr. Michæl Dryden
It seems no matter what we do, they are still here. They are able to survive our insecticide assaults. They have a biological capacity to stay one step ahead of us. I find that very fascinating.

There has been remarkable change in the ecology of these ticks in the last 20 years. It relates to a number of factors, including climatic change, milder winters and reforestation in the eastern United States. It relates also to a substantial increase in wildlife populations because of our conservation efforts. White-tailed deer, wild turkey and coyote are the three big ones that have substantially changed our tick populations.

At the beginning of the 1900s, we were down to a population of about 300,000 white-tailed deer in the United States. We are now at a population of over 30 million. Deer are a primary reproductive host to two very important tick species — the Lyme disease tick Ixodes scapularis and the Lone Star tick Amblyomma americanum.

Climate change, wildlife population and reforestation have allowed a dramatic shift in the tick population, distribution and density. It is a well-published phenomenon in the scientific community.

DVM: How frustrating is compliance when it comes to parasite treatment and prevention?

Dryden: We all struggle with this. When that pet owner brings a dog or cat into a practice, the fleas on it came from flea eggs laid three to eight weeks ago. Most pet owners think their dog or cat got the fleas from another dog or cat.

Most also think that the fleas biting them came off their dog or cat. It is completely erroneous.

We have to help pet owners recognize that their pet had fleas last month or two months ago. Those fleas laid eggs, and we are now dealing with the life cycle.

The pet owner frequently comes back and says, 'My pet didn't have fleas last month.' The reality is the pet did have fleas; they just didn't notice it. The vast majority of pet owners never see the first fleas their dog or cat gets. Those female fleas lay 40 to 50 eggs a day. Now we are dealing with control of second and third generations. The end result is the household is infested, and the environment is saturated with all different life stages.

I often hear it: 'If I put the product on today, the fleas will be gone tomorrow.' That is not going to happen because the environment has been seeded. You have to try to change that thought process. Most problem-flea cases are due to a significantly contaminated environment, and pet owners are going to have to work to control it for the next month or so.

When a pet owner says a product doesn't work, you have to think about compliance. Or, they might be lying or exaggerating about their efforts to control the flea infestation.

The regular monthly application of these products probably is the biggest issue we address from a compliance perspective. Some pet owners simply don't apply these products as regularly as they need to, and/or they often don't administer them correctly.

An owner may administer them for one or two months until the fleas appear to be gone. They stop treatments, and then they are upset when fleas come back.